A distributed file system is a system in which files are shared among a plurality of servers via a network. In a distributed file system, each client accesses a shared file via a file server. Because of this, distributed file systems have a problem such that accesses concentrate in the file server if the number of clients using the system increases. The file server is requested to have a high performance in order to process concentrated accesses.
However, introducing a high-performance server into the system is not favorable from the viewpoint of cost reduction. Because of this, a technique is known for reducing the amount of processing in the file server by distributing the load imposed on the file server.
As an example of a technique related to load distribution, a technique is known for making an attempt to reduce the load on the server by using a memory on the client side as a cache so as to increase the amount of processing on the client side (e.g., see Non-Patent document 1).
As another example of a technique related to load distribution, a technique is known for starting communication by command issuance from the client side. This technique is called, for example, RDMA (Remote Direct Memory Access). This is the technique for reducing the load accompanying issuance of a command to the NIC on the server side (e.g., see Non-Patent document 2).
As a related technique, a technique is known for performing data communication by using DMA (Direct Memory Access). Setting a shared memory so that an end point has an address range within the shared memory by establishing a transaction-oriented protocol between a host system and the end point is known (e.g., see Patent document 1).
As another related technique, it is known that each device transfers information of an interrupt factor register to the main memory by using DMA. It is known that the main storage device has an address allocated to each device in advance and the device writes DMA to the allocated address (e.g., see Patent document 2).    Patent document 1: Japanese Laid-open Patent Publication No. 2008-152783    Patent document 2: Japanese Laid-open Patent Publication No. 11-312138    Non-Patent document 1: Michael D. Dahlin, Randolph Y. Wang, Thomas E. Anderson, David A. Patterson, “Cooperative caching: using remote client memory to improve file system performance” OSDI '94 Proceedings of the 1st USENIX conference on Operating Systems Design and Implementation, Article No. 19 USENIX Association Berkeley, Calif., USA@1994    Non-Patent document 2: Kostas Magoutis, “The Optimistic Direct Access File System: Design and Network Interface Support”, Proceedings of the 1st Workshop on Novel Uses of System Area Networks, 2002